Automatic flush on exit

[vaind]

We should find a way to send messages asynchronously while still actually trying to send them before the script exits.

• trap only gets triggered for errors so that is not usable
• Register-EngineEvent -SourceIdentifier Powershell.Exiting -Action {} gets stuck on Stop-Sentry call indefinitely. Also, it doesn't seem to work reliably

For now, I'm doing what we do in webGL in Unity, i.e. implement a synchronous "background" worker instead of an async one.